It is well known that exhaust gas recirculating (EGR) operation in an internal combustion engine, to decrease the amount of nitrogen oxides (NO.sub.x) in the engine exhaust, causes inferior flame propagation velocity in the combustion chamber of the engine. Therefore, it is necessary to advance the ignition timing during EGR operation to obtain maximum output power and maximum fuel consumption efficiency.
To this end it is already known to provide such apparatus with a vacuum advancer having a diaphragm mechanism to control the vacuum ignition timing in response to the negative pressure in the carbureter when the EGR is in operation.
However, this type of apparatus has the disadvantage that vacuum ignition timing during engine acceleration is advanced, when there is no necessity for it. To advance the ignition timing during acceleration causes substantially increased amounts of NO.sub.x in the exhaust.